This invention relates generally to offshore drilling operations.
Offshore drilling operations may be implemented with a variety of different platforms which may be secured to the seabed floor. These platforms may be effective at shallower depths. At greater depths, such as depths greater than 5000 feet, it is generally desirable to use ships or semi-submersible rigs to conduct such deep water drilling operations.
These ships or rigs may be precisely positioned at a desired location so that the drilling equipment may be operated to precisely drill wells at desired locations. The ship or rig may be maintained in position under dynamic positioning even in extreme seas. As used herein, a “ship” is a floating platform capable of propulsion on its own or by being pushed, pulled or towed. It includes semi-submersible rigs and self-propelled vessels.
As a result, a number of exploration wells may be drilled, one after the other, in a deepwater offshore environment, such as the outer continental shelf of the United States, Africa, Asia, or Western Europe. However, the large number of operations that must be performed when successively drilling a number of exploration wells, even in the same area, may be extremely time consuming because of the complexity of deep water operations.
Conventionally, tubulars must be made up, lowered through extensive sea depths to the seabed floor, used to drill the seabed floor, and then withdrawn to be replaced by other tubulars. As used herein, “tubulars” refers to piping, conduits, conductors, casing, drill strings, and risers. In addition, marine risers must extend ultimately from the ship to the seabed floor and blowout preventers may ultimately be run and installed on the seabed floor for well control reasons. Assembling, positioning, and removing these disparate tubulars generally involve operations that take extensive time periods. The time needed to extend a tubular through 5000 or greater feet of water results in some delay. The time needed to make up tubulars results in additional delay.
With a conventional ship having a single drilling platform, it is impossible to perform multiple operations in parallel. Thus, the time periods needed to complete each well may be relatively long. Since, generally, these drilling ships are operated on a rental basis, the longer that it takes to drill the well, the more expensive is the resulting well.
So called dual activity drilling ships are known. In these ships, a pair of derricks may be provided on the ship which provide a structural support for underlying drilling tubulars. The dual derricks may be operated in some degree in parallel. For example, while one operation is occurring on one derrick, other operations may be implemented on another derrick. While such approaches may result in some time savings, there are still some deficiencies in such dual activity approaches.
Thus, there is a need for even faster ways to drill deep water wells.